This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 02079713.0 filed in Europe on Nov. 7, 2002, which is herein incorporated by reference.
1. Field of the Invention
The present invention is relates to a printing device such as a printing or copying system employing multiple print heads containing discharge elements for the image-wise forming of dots of a marking substance on an image-receiving member. Examples of such printing devices are inkjet printers and toner-jet printers.
2. Related Art
Print heads employed in inkjet printers and the like usually contain a plurality of discharge elements arranged in (a) linear array(s) parallel to the propagation direction of the image-receiving member or in other words the sub scanning direction. The discharge elements usually are placed substantially equidistant. In operation, the discharge elements are controlled to the image-wise discharge of ink droplets on an image-receiving member to form columns of image dots of ink in relation to the linear arrays. The discharge activation may be thermally or thermally assisted and/or mechanically or mechanically assisted and/or electrically or electrically assisted, including piezoelectrically. In scanning inkjet printers, the print heads are supported by a print carriage which is movable over a guide member across the image-receiving member, i.e. in a direction perpendicular to the propagation direction of the image-receiving member or in other words the main scanning direction. In operation a scanning inkjet printer forms a matrix of image dots of ink corresponding to a part of an image by scanning the print heads at least once, optionally bi-directionally, over the image-receiving member in the main scanning direction. After a first matrix is completed the image-receiving member is displaced so as to enable the forming of the next matrix. This process may be repeated till a complete image is rendered.
Alignment of the print head(s) in inkjet printers, particularly in the sub scanning direction, is of the utmost importance as dot positioning errors may cause visual disturbances in the formed image. In scanning inkjet printers having multiple print heads, contiguous dots may originate from different print heads. Examples of such inkjet printers include multi-color printers having at least one print head per color, and multi-color printers having at least one print head for the black process color and at least one print head for the other process colors, and monochrome printers having multiple print heads for the black process color. Not only alignment of the respective print heads in such printers, particularly in the sub scanning direction is of utmost importance, but also accurate positioning of the print heads relative to each other. The alignment of the respective print heads relative to each other in the sub scanning direction can be controlled by accurately positioning the print heads with respect to a reference position. This reference position is typically the guide member, on which the print carriage assembly supporting the print heads is suspended. This is a challenging problem as the positioning accuracy should be in the range of several hundreds of micrometers, preferably several tens of micrometers, while the distance between the guide member and the respective print heads is typically in the range from a few centimeters to several tens of centimeters.
An approach to tackling this problem is providing a print carriage assembly containing built-in means for mounting the respective print heads to the assembly. As this built-in mounting means is located at fixed positions within the assembly, the position with respect to the points of suspension of the assembly is also determined. Therefore the positioning accuracy of the print heads depends on the dimensional tolerances used to manufacture the print carriage assembly. Consequently, to obtain a high positioning accuracy for the respective print heads, the print carriage assembly should be manufactured with a high degree of precision, i.e. the respective parts and/or components of the assembly should be manufactured and positioned using dimensional tolerances typically in the order of micrometers or less. Although it may be possible to manufacture print carriage assemblies with such stringent dimensional requirements, the costs involved would be too high to be of commercial use.
In European patent application EP 1145860, a print head assembly is disclosed which may be easily installed and removed from a fixed position on the printer wall via a snap-fit arrangement using resilient side-fingers.